The invention disclosed herein broadly relates to asset management systems, and more particularly to a system for tracking the real-time location and status of vehicles of a fleet, and for communicating between the vehicles and a dispatcher or expediter in the fleet offices.
Operators of fleet vehicle businesses need to know where each vehicle in the fleet is located and what it is doing in order to make decisions on how to use the vehicles most efficiently. In recent years, vehicle locating systems have been developed using Global Positioning System (GPS) satellite information, and, for greater accuracy, differential GPS (DGPS) systems. These systems are highly accurate where line of sight (LOS) conditions exist, that is, where the vehicle (or more accurately, the vehicle""s GPS receiver) has a clear LOS to the appropriate number of GPS satellites. But such conditions are typically unavailable or are at least less frequently available for a vehicle operating on city streets, particularly in areas where multi-story buildings are present, owing to the shielding that such buildings effect. In those circumstances an alternative navigation system such as dead reckoning (DR) navigation may be used to provide vehicle position and velocity data in urban canyons (i.e., streets bordered by tall buildings) where GPS measurements are only intermittently available. Or a map matching technique or navigation grid may be used as another or additional alternative.
Currently, wireless voice communication between dispatchers and drivers is the primary means of addressing the need of the fleet owner or operator to know what each vehicle is doing, i.e., its operations taking place at any given time, and where the vehicle is located when a particular operation is occurring. In industries where vehicles perform a repetitive sequence of events with each load, such as for ready mix concrete operations, xe2x80x9cstatus boxesxe2x80x9d have recently come into use. The status boxes require the driver to press a button at each stage of operation such as xe2x80x9cload,xe2x80x9d leave plant,xe2x80x9d xe2x80x9carrive job,xe2x80x9d xe2x80x9cbegin pour,xe2x80x9d and so forth.
The primary problem with either wireless voice communication or status box systems is that data are manually provided to the dispatcher from the driver of the vehicle. This leads to untimely (late) and, perhaps worse, inaccurate data more than ninety percent of the time, according to analyses performed by the fleet owners/operators. The availability of timely, accurate data is essential if the fleet operator is to operate its business efficiently and economically.
Time Division Multiple Access (TDMA) wireless networks, which are in use for many applications including digital cellular telephones and wireless local area networks, may be used for the communication between dispatchers and drivers. A TDMA network allows multiple users of a single channel or frequency by assigning specific time slots to each user to use exclusively for transmission. For optimal performance of TDMA networks, precise time synchronization between members of the network is required. Efficient use of bandwidth in the network requires that the gap times between transmissions of each user, which is wasted time, be minimized. An important component to the gap time is uncertainty of time in all the participants in the network. Synchronization of wireless networks is often very coarse, requiring large gaps between transmissions, if specialized hardware is not used. Moreover, synchronization of network elements to a precise reference like GPS based timing information involves having a GPS receiver located on each network element, both mobile and fixed, increasing installation costs and complexity for both fixed network infrastructure and mobile network devices, especially if navigation data provided by GPS is not required.
Precise time synchronization between all of the wireless devices in the network can be performed in a number of ways. Typically, a precise, stable time reference, such as one based on the Global Positioning System (GPS) or other time distribution services, is located within each wireless device or within just the fixed infrastructure of the network, with synchronization information being transmitted to the mobile units. In these cases, device or infrastructure costs are increased because timing equipment has to be distributed among several locations or devices and installed where space and access for maintenance are limited.
Transmitting as much information as possible in a given amount of bandwidth is an important design goal in any communications network. This is especially true in wireless networks in which available bandwidth is very limited and customer requirements for data throughput are immense. Operation on most wireless bands is subject to occupied bandwidth constraints, requiring the data signal to be contained in a vary narrow region of the electromagnetic spectrum. In TDMA networks, a challenge is to minimize the gap times between transmissions and the overhead associated with each data packet in order to send as much information bearing data over the network as continuously as possible. The present invention addresses these two requirements with digital filtering to control occupied bandwidth and data recovery by the receiving system that requires no synchronization patterns to be transmitted.
The primary goal of the fleet management system of the present invention (sometimes in hereinafter called the PROTRAK system or the Galileo system (each of PROTRAK and Galileo, either alone or with various suffixes attached, is a trademark of Fleet Management Services, Inc. of Chandler, Ariz., to which the present patent application is assigned), the fleet management system, or simply the system) is to provide fleet management information to customers (i.e., the owners, operators, subscribers, or users of the fleet who seek to avail themselves of the advantages of a vehicle tracking, communication and fleet management system) to enable them to manage their assets more profitably. The system provides its customers with several means to accomplish this. First, the PROTRAK system gives the fleet operator the capability to locate vehicles of the fleet in real-time. Second, the system allows the operator to communicate with those vehicles over a very efficient and reliable wireless networkxe2x80x94a time division multiple access (TDMA) wireless network. Third, the system enables the operator to receive timely, accurate data regarding what each vehicle of the fleet is doing, i.e., what operation(s) it is performing at any given time. Fourth, the system provides the operator with an ability to correlate the position and messaging information generated by the system with the operator""s other management information systems to provide an integrated information source for improved fleet business management.
With respect to the latter, a fleet operator""s existing management systems typically consist of accounting, human resources, inventory, and other systems which may not be well integrated. In addition, the operator may not have a reliable way to measure vehicle and driver performance which is critical to the operator""s operations. The PROTRAK system provides the required vehicle and driver information together with a database management system that is capable of collecting such information and integrating it with data retrieved from the operator""s other information systems in a database management application. This application can be used by the operator to generate reports that are tailored to its business and are based on all of the available data.
The PROTRAK system is particularly designed to operate in a market niche between cellular, specialized mobile radio (SMR), and paging services. The system may be used to track virtually any number of vehicles in a fleet across all metropolitan areas covered by the network.
Timely, accurate data can be made available to the fleet operator automatically by combining wireless data network technology, a wireless data computer (also referred to herein as a tracking computer, or simply a tracker), sensors, and dispatch and/or database reporting software and computers at the fleet operator""s facilities to receive, display, and process the data provided by the vehicles. The vehicle computer has interfaces to various sensors that indicate operations being performed by the vehicle. Data provided by the sensors are processed by software algorithms in the computer to determine when events of interest occur. The event, relevant parameters, and the time of the event are then immediately transmitted through the wireless network to the fleet operator.
The network used to enable event driven status reporting is designed to provide frequent small packets of data from vehicles to fleet owners very efficiently. The network architecture is a unique, full duplex design for metropolitan area operations. Data are transmitted to vehicles over a subcarrier on an FM radio station. Vehicles transmit their data using a TDMA protocol on a single UHF channel. Vehicle data are received by Network Hubs, which are receivers placed on commercial towers around the metropolitan area of interest. The received data are sent back to a Network Distribution Center (NDC, occasionally referred to herein as Network Control Center) via telephone lines and are relayed to the fleet owners via the Internet, telephone connection, or other preferably wireless means. Data sent to the vehicles by the owners is first sent to the NDC which sends it to transmitting equipment at the radio station via telephone lines.
The TDMA protocol in the network is controlled by servers in the NDC. The precise timing required by the TDMA network for efficient operation is controlled by a synchronization pattern contained in the subcarrier data broadcast that is received by the vehicles and the network hubs within the PROTRAK system. This enables all vehicles and hubs to have a common time reference that is accurate to about three microseconds. This, in turn, enables a multiplicity of (e.g., 50)vehicle reports in the TDMA network each second. The servers assign reporting intervals and time slots to vehicles so that they can send data and status changes automatically. Typical periodic updates of navigation data or other non-critical information are provided at two to three minute intervals; it is impractical for the vehicle computer (tracker) to wait for a periodic interval of that length to send time critical event data.
A total of 50 20-msec long time slots are available for periodic transmissions. Multiple vehicles share slots, the number depending upon the update rate of the slot. For example, 60 vehicles can share a one minute update interval slot. Slots not assigned to periodic updates are open for any vehicle to use to request access to the network. If more than one vehicle tries to use the same interval in a particular slot, both may still be heard if each is heard by a separate hub receive site. Otherwise there is a collision (interference) of data, and the vehicles involved must retry their requests.
According to an aspect of the invention, a method and apparatus are disclosed for automatically determining and reporting events from a vehicle to an owner or dispatcher of the vehicle at a remote location. Events to be reported are changes in status of vehicle operation, location, or measurements of vehicle systems or cargo. A computer (tracking computer, generally referred to herein as the tracker) installed on the vehicle is connected to various sensors which measure parameters of interest to the dispatcher or owner and reports critical changes in parameters over the wireless TDMA network. Computers at a fixed location display these status changes for use by the dispatcher or record the data for later analysis. Software in the tracker in the vehicle together with data supplied by what may be a small number or a wide variety of sensors allows multiple, complicated, and abstract status events that are relevant to specific vehicle or industry applications to be determined and reported by the tracker. Automatically generated reports from the trackers provide more accurate and timely data to the fleet management offices of the customer than is available from the drivers of the vehicles.
The tracking computer has navigation hardware and software for determining the location, speed, and direction of travel of the vehicle in which it is installed. The application software used by operators to receive data from their vehicles also enables them to send xe2x80x9csite dispatchxe2x80x9d commands to the trackers which indicates a rectangular region to be used to indicate where events such as xe2x80x9cload,xe2x80x9d or xe2x80x9cunload,xe2x80x9d for example, should take place. Location information is then combined with the sensor data in the algorithms to determine event sequencing, provide exception reporting to indicate that the vehicle performed a specific action at the wrong location, performed unauthorized stops on the way to or from a job, or other events specific to a particular business or industry.
In an exemplary embodiment of this aspect or feature of the invention, three basic components are combined to enable vehicle data to be useful to the fleet operator, namely: (1) sensors on the vehicle to measure parameters to be combined in a computer to automatically determine when events of interest occur, (2) a wireless network that allows prompt, economical transmission of small packets of data containing event status to the fleet operator, and (3) software applications to store and further process event information for improved asset management by the fleet operator.
The tracker has several inputs and outputs to allow it to sense and control numerous vehicle functions simultaneously, with configurable interfaces that include serial interfaces, analog inputs, discrete inputs, discrete outputs, and an interface for pulse measurement or clock outputs. The tracker also has dedicated interfaces for measuring battery voltage, ignition, speed, and reverse. These enable measurement of a wide variety of vehicle functions, either directly or through auxiliary sensor modules that provide data to the computer serial interfaces. The outputs allow control of vehicle functions remotely, through the wireless network.
Tracker software permits processing and integration of various sensor inputs to enable higher level or abstract status events to be determined and reported. For example, in a xe2x80x9cloadingxe2x80x9d status for a ready mix truck, a loading is determined from a number of inputs by combining truck location at the plant, truck stationary, and truck drum rotating in the charge direction at a speed greater than a predetermined minimum speed for a minimum time interval. Examples of other status events include xe2x80x9cambulance emergency lights onxe2x80x9d or xe2x80x9cfour wheel drive engaged,xe2x80x9d which, as with other simpler status events, are simply detected and reported.
The tracker reports events over the wireless network whose architecture and protocols are tailored for prompt reporting of events while concurrently supporting slower, periodic update intervals for less critical data. As noted above, the network uses a TDMA protocol to enable a large number of vehicles to send short data packets frequently on a single wireless channel. Data is sent to the vehicles over a subcarrier on an FM broadcast channel. An important aspect of the invention is the provision of precise time synchronization required for the TDMA protocol over the FM link to the vehicles and receive sites. In the exemplary embodiment, as many as fifty vehicles per second can report data at a variety of update intervals ranging between five seconds and one hour.
Typical periodic updates of navigation data and other non-critical information are provided at two to three minute intervals. However, it is not practical for the tracker to wait for periodic intervals of that length to send time critical event data. Accordingly, for such events, the network maintains a number of time slots for additional access to the network on request of any vehicle needing to transmit event data. The requesting vehicle is then granted sufficient auxiliary reporting times at twelve second intervals to send its data. The total latency between an event being detected and the transmission of data is kept under thirty seconds.
Owners and dispatchers of fleet vehicles are provided with computer software applications that enable connection of their desktop PC""s to the TDMA network using the Internet or other means. Data furnished from the vehicles are routed to these applications by the network servers, and are also stored in a local database. One of these software applications allows viewing the vehicle locations as icons on a map displayed on a monitor, showing event changes for each vehicle on the map in real time as they occur, and also enables the dispatcher to send messages or dispatch locations to the vehicles. Automated events may be provided as well to other dispatch or vehicle management applications, as required. Advantageously, these applications integrate vehicle event data with other systems utilized in the fleet operator""s business, such as order entry and call management. Reports on vehicle events may be generated from these applications over the Internet from data stored in the network database.
According to another of its aspects, the present invention minimizes infrastructure cost for time references in the TDMA wireless network and locates the time reference in a central network control facility that is easily maintained and monitored. The time reference uses GPS referenced time, and TDMA network time is held in synchronization to the GPS reference by a wireless phase lock loop (PLL), removing the requirement to locate the time reference within the wireless transceiver devices or infrastructure elements. This aspect of the invention enables precise time synchronization of all wireless network elements by using special timing hardware and by distributing a single, remote GPS based time reference throughout the network using a wireless PLL. Digital data is remotely synchronized in the TDMA network, a full duplex system designed to efficiently transmit short bursts of data from mobile vehicles to their owner on a frequent basis. Vehicles transmit data using a TDMA protocol in the UHF frequency band in precisely controlled time slots at a rate of 50 vehicles per second. Vehicles send location, status, and message data to the fleet owners or dispatchers who are connected to the wireless network through the Internet or other means. Data transmitted to the vehicles is broadcast over a subcarrier of an FM radio station, including network timing and control information as well and messages and information from fleet operators.
Timing of the TDMA portion of the network is controlled from a central network control facility that houses the servers which control vehicle access to the network and manage fleet owner connections to the network. Synchronization of the vehicle devices and fixed hub receiver systems that receive vehicle data is maintained through synchronization information contained in the FM subcarrier broadcast. The FM subcarrier timing data is, in turn, referenced to a GPS based time source at the network control center.
A Subcarrier Control Computer (SCC), responsible for providing the data to the subcarrier modulator, is located at the FM radio station transmitter or studio facilities. It clocks the transmit data at precise intervals based on timing commands from a Network Timing Control Computer (NTCC), located at the network control center. The NTCC and SCC are connected through a modem for data and timing control commands sent to the SCC. The NTCC computes timing commands based on the synchronization information from a GPS receiver time reference and that from an FM subcarrier receiver which receives data from the SCC. The difference in time from the GPS time reference and the received synchronization data over the FM subcarrier is processed by the NTCC using a PLL algorithm to generate a timing correction which is sent to the SCC.
This wireless PLL timing control loop enables a single, remotely located time reference to synchronize the TDMA network. In addition, the feedback inherent in the control loop allows the system to compensate for variations in FM radio station group delay so that the broadcast synchronization data is applicable at the FM antenna. This is important for large networks based on this technology that require multiple FM stations to cover overlapping geographical areas, because it enables the FM stations to be synchronized.
The invention also relates to bandwidth optimizations for the transmission of data over wireless TDMA data networks. The invention minimizes occupied bandwidth in a wireless channel by digitally filtering the data to be transmitted before modulation. The filter is implemented in a low-cost microcontroller, which replaces each edge in a digital square wave data stream with transitions that have the shapes of rising or falling sine waves. This has the advantages of reducing higher harmonics in the data signal, especially at the highest data rate, where the square wave is effectively replaced by a sine wave. Another aspect of the invention maximizes the efficiency of the TDMA network by refraining from sending any special bit synchronization information in addition to the data. In most systems, a large number of bits is devoted to synchronization, framing, or data clock recovery. In one aspect of the present invention, the bit clock and data synchronization are performed by the receiver by using forward error correction algorithms, special bit interleaving, and high performance digital signal processing hardware and software. Still another aspect of the invention uses space diversity combining between multiple receive sites to improve the reliability of receiving data. More reliable data reception saves bandwidth by reducing the number of retries required to move data through the network.